Etiology PRIMARY HYPOTHYROIDISM Hoshimoto' s thyroiditis-most common Irradiation of thyroid Su urgical removal Late stage invasive fibrous thyroiditis Iodine deficiency Drug therapy lithium) Infiltrative diseases Sarcoidosis, amyloidosis Scleroderma hemochromatosisEtiology PRIMARY HYPOTHYROIDISM Hoshimoto’s thyroiditis-most common Irradiation of thyroid Surgical removal Late stage invasive fibrous thyroiditis Iodine deficiency Drug therapy (Lithium) Infiltrative Diseases: Sarcoidosis, Amyloidosis Scleroderma, Hemochromatosis